1. Field of the Invention
The present invention relates to a method of fabricating a nano-tube that is suitably used for manufacturing a field-emission type cold cathode that is used as an electron source of a planar panel display, CRT, electron microscope, electron-beam exposure device, various electron-beam devices, etc. The invention also concerns a method of manufacturing the field-emission type cold cathode, as well as a method of manufacturing a display device.
2. Description of the Related Art
Attention has in recent years been drawn toward a carbon nano-tube as emitter material of a field-emission type cold cathode. Applications of the carbon nano-tube have been expected to occur and research and developments thereof have also been vigorously performed.
The carbon nano-tube is a type obtained by rounding a graphen sheet having carbon atoms regularly arranged, a planar graphite hexagonal net, into a tube-like configuration. Depending upon the diameter of the tube and the chiral angle, the electronic structure is largely varied. Therefore, the co-efficient of electrical conduction has a value between a metal and a semiconductor.
Therefore, it is the that the carbon nano-tube exhibits characteristic in that an electrical conduction thereof being close to one-dimensional electrical conduction.
This carbon nano-tube is a minute material, the diameter of that is in the order of nano-meters, the length of that is from 0.5 xcexcm to several millimeters, and an aspect ratio of that is very high. For this reason, electric field is easily concentrated at end tip portion of the carbon nano-tube and thereby it is expected that a high level of emitted-current density can be obtained.
Also, the carbon nano-tube has the feature of having a high level of chemical and physical stability. Therefore, it can be presumed that, during its operation, the carbon nano-tube would not be adversely affected by the adsorption of residual gases, ion impact or the like, in a vacuum, easily.
FIG. 7 is a sectional view illustrating an example of a conventional field-emission type cold cathode, wherein the carbon nano-tube is used as the field-emission type cold cathode. It is to be noted that this type of field-emission type cold cathode is disclosed in the Japanese Unexamined Patent Publication (KOKAI) No. 9-221309.
This field-emission type cold cathode has a substrate 24 including carbon therein, on which a carbon nano-tube 26 to be used as an emitter, is formed by radiating ions onto the substrate 24. Further, gate electrodes 28, 28 and an insulating layer 27 are formed so as to surround the carbon nano-tube 26.
A grid 29 through which an electron beam is drawn out, is formed so as to oppose the carbon nano-tube 26.
The carbon nano-tube 26 has a diameter of from 2 to 50 nm and has a length of from 0.01 to 5 xcexcm.
In this field-emission type cold cathode, an emission current of 10 mxc3x85 is caused to occur with a voltage of 500V.
In this field-emission type cold cathode, the insulating layer 27 and the gate electrode 28 are formed so as to surround the carbon nano-tube 26. Therefore, the amount of electrons that are emitted from the emitter can be controlled by an electric field that is formed applied between the gate and the emitter. Here, the electric field between the gate and the emitter is approximately equal to a value obtained by dividing the voltage applied to the gate by the thickness of the insulating layer 27.
Note that, in case the thickness of the insulating layer 27 is large, it is necessary to apply a high level of gate voltage. However, in case the thickness of the insulating layer 27 is small, the same emission current can be obtained with a small gate voltage.
On the other hand, the electrons that have been emitted from the emitter each have a kinetic energy acting into a direction perpendicular to the electron emitting direction, depending upon the gate voltage. Therefore, the direction of the emission path of the emitted electrons are spread out.
In case of the gate voltage being low, it is possible to obtain an electron beam relatively highly bundled or having high level of coherency.
However, as the gate voltage becomes high, the degree of divergence of the electrons in the beam increases.
For example, in a planar display device in that a plurality of pixels are independently controlled, the divergence of the emitted electrons mean that the electrons directed toward one pixel, impinge upon an adjacent pixel. Thereby, the inconvenience in that an image becomes blur, or the contrast thereof is degraded or the like, will be caused to occur.
Accordingly, a decrease in the thickness of the insulating layer 27 is an indispensable factor for realizing a decrease in the drive voltage, a reduction in the size and cost of the drive circuit, a suppression in the spread of the electron beam or the like,
FIGS. 8(a) and 8(b) illustrate an example of a conventional planar display device, FIG. 8(a) being a perspective view and FIG. 8(b) being a sectional view. This planar display device is disclosed in the Japanese Unexamined Patent Publication (KOKAI) No. 10-199398.
In this planar display device, on a glass substrate 34, rectangular cathodes 35 made of graphite and having a thickness of 1 xcexcm and an insulating layers 37 made of a silicon oxide film and having a thickness of 7 xcexcm, and width thereof being 20 xcexcm, are stacked with each other.
On the cathode 35, there is deposited using an arc discharge technique, a laser ablation technique or the like, a carbon nano-tube 36 having a rectangular configuration and having a thickness of several xcexcm and that becomes an electron emission layer arranged in a line.
On the rectangular carbon nano-tube 36, there are provided grid electrodes 38, through which the electrons are drawn out, in such a way as to cross the carbon nano-tube 36.
The carbon nano-tube 36 has a diameter of from 10 to 40 nm and a length of from 0.5 to several xcexcm.
In this planar display device, applying a positive voltage to the grid electrode 38 and applying a negative voltage to the cathode 35 cause electrons 39 to be emitted in the arrow-indicated direction as shown in FIG. 8(b).
FIG. 9 is a sectional view illustrating an electron-source array that is another example of the conventional field-emission type cold cathode, and that is disclosed in the Japanese Unexamined Patent Publication (KOKAI) No. 10-12124.
This electron-source array is the one wherein a carbon nano-tube 46 is grown in each of the fine holes 42 of an aluminum film 45.
This electron-source array is manufactured as follows. First, the aluminum film 45 is deposited on a glass substrate 41. This aluminum film 45 is etched to thereby form an element isolation region 44 within the aluminum film 45. The remaining aluminum film 45 is used as an emitter region.
Subsequently, anodic-oxidation treatment is performed on the aluminum film 45 to thereby form the fine holes 42. Thereafter, in each of the fine holes 42 there is buried a nickel particle 47 that becomes a nucleus of growth of the carbon nano-tube.
Thereafter, the nano-tube 46 is grown in an atmosphere containing therein methane gas and hydrogen gas. The reaction temperature at this time is ranging from 1000 to 1200xc2x0 C.
With the use of the above-described procedure, it is possible to grow on the glass substrate 41 the carbon nano-tube 46 that has orientation in the vertical direction with respect to the substrate 41. And, by attaching a grid electrode 48 onto an upper portion of the aluminum film 45, it is possible to manufacture a field-emission type cold cathode.
Also, a phosphor 49 is disposed at a position that opposes a plurality of emitters, i.e., carbon nano-tubes 46, each of which is isolated from each other by respective element isolation region 44 to thereby fabricate a planar display device.
Further, as an example of the method of fabricating a carbon nano-tube, there has also been proposed a method that includes a step of disconnecting part of the bond of each of the carbon atoms constituting the carbon nano-tube. The step thereby forms a non-bonded electron (dangling bond) (refer to the Japanese Unexamined Patent Publication (KOKAI) No. 7-172807).
In this method, a gold ion (Au+) was used as an example, a crater structure is formed by one ion radiation. For example, selectively radiating a large number of ions onto the carbon nano-tube so as to cross over the carbon nano-tube, a plurality of crater structures are successively formed. And these crater structures are connected with one another, thereby the carbon nano-tube is disconnected.
Meanwhile, in the conventional field-emission type cold cathode illustrated in FIG. 7, in realizing an excellent electron-emission characteristic by making the insulating layer to have a thin thickness, the following problems arose.
(1) Flattening the surface of the emitter is difficult.
The carbon nano-tube obtained using the arc discharge technique or laser ablation technique that is a general carbon nano-tube manufacturing method, generally has a substantially constant value in diameter that is in an order of nanometers.
However, the length thereof shows various values raging from 0.5 xcexcm to several mm. Also, because the carbon nano-tube has a high flexibility, it has the feature of one nano-tube being easily entangled with each other. Therefore, when the long carbon nano-tubes are entangled with each other, they get shaped like a large yarn junk. This causes a decrease in the flatness of the emitter.
Also, the coarse carbon nano-tube after the same has been produced contains therein graphite, amorphous carbon or the like, In case of especially a mono-layer carbon nano-tube, it contains a metal catalyst. The carbon nano-tube can be easily entangled with such impurities as well to thereby form a large mass.
It results in that local protrusions will occur on the surface of the emitter. These local protrusions cause to form a curvature in the insulating layer 57 and gate electrode 58 formed on the carbon nano-tube 56 on the substrate 54 and make the potential distribution non-uniform as illustrated in FIG. 10.
Also, when the local protrusions are produced at the opening portion of the gate, the electric field is easily concentrated at this portion, reducing the uniformity of the electron-emission characteristic thereof deteriorated.
Furthermore, in the planar display device wherein a plurality of emitters are two-dimensionally arrayed, those large protrusions make the characteristic of one of the emitter portions, i.e., the pixels, different from those of other emitter positions (the pixels).
This causes unevenness in the image.
(2) The gate electrode and the emitter are electrically conducted to each other via the carbon nano-tube.
In case the carbon nano-tube having a length larger than the thickness of the insulating layer exists on the surface of the emitter, that carbon nano-tube contacts with the gate electrode 58. There is resultantly the case where the gate electrode 58 and the carbon nano-tube 56 serving as the emitter electrically conduct with each other.
This short-circuit between the carbon nano-tube 56 and the gate electrode 58 becomes a cause of the decrease in the amount of electrons emitted and a cause of the destruction of the elements. As in the case of the above-described problems under the item No. (1), that short-circuit of the gate electrode and the emitter becomes a factor that causes the electron-emission characteristic to become non-uniform. Especially in the planar display device, the short-circuit makes the image uneven in many positions and also makes the image unstable.
In this field-emission type cold cathode, the length of the carbon nano-tube 26 is ranging from 0.01 to 5 xcexcm. However, for example, in case the thickness of the insulating layer 27 is 5 xcexcm or less, as described above, there is a possibility that the gate electrode 28 and the emitter will be short-circuited by way of the carbon nano-tube 26. Or there is also a possibility that a mass of carbon nano-tube, having a length L being large, will locally occur inside the gate opening.
Also, in the conventional planar display device as well that is illustrated in FIG. 8, in case in that a large number of carbon nano-tubes each having a length being larger than the thickness (7 xcexcm) of the insulating layer 37, are contained therein, the same problems arise.
Further, in each of these two conventional examples, the carbon nano-tube is grown directly on the substrate. Therefore, it is difficult to control the length of this carbon nano-tube. Accordingly, in these conventional examples, realizing a uniform electron emission characteristic is difficult, which means that a limitation is imposed upon making a thickness of the insulating layer, thin.
Also, in the conventional electron-source array illustrated in FIG. 9, it is certainly possible to grow the carbon nano-tube 46 with a high control-ability in the direction perpendicular to the surface of the glass substrate 41. However, the growth temperature of the carbon nano-tube 46 is approximately 1000xc2x0 C. and the relevant steps for forming same, are complex. Therefore, this technique is unsuitable for manufacturing a planar display or the like, wherein a plurality of emitters are formed on the glass substrate 41.
Also, in the conventional fabricating method of carbon nano-tube, because use is made of a convergent ion source, there was the problem that a long time was needed to cut off the carbon nano-tube through the entire surface of the emitter. Also, in an ordinary ion implantation, in case radiation has been performed until the carbon nano-tube is cut off, ions cause damage even to the portion that is not to be cut off. Resultantly, there was the problem that the most part of the carbon nano-tube became unable to have its annular shape maintained as it was.
The present invention has been made under the above-described draw-backs and has an object to provide a method of fabricating a nano-tube that enables cutting off the nano-tube in a short length without deteriorating the same and that, when using this nano-tube as the emitter, provides an improved flatness of the surface thereof.
Another object of the invention is to provide a method of manufacturing a field-emission type cold cathode that can provide an improved flat-ability of the emitter surface and that can therefore cause an emission of a uniform, stable high-emission electric current.
Still another object of the invention is to provide a method of manufacturing a display device that includes the above-described fabrication method of nano-tube and/or manufacturing method of a field-emission type cold cathode.
To attain the above object, the present invention has provided the following nano-tube fabrication method, field-emission type cold cathode manufacture method, and display device manufacture method.
Namely, a fabrication method of a nano-tube according to the first aspect of the invention comprises the step of radiating ions onto the nano-tube, and oxidizing the nano-tube.
In this fabrication method of a nano-tube, with a very much simplified method, the nano-tube has been provided with a non-bonded hand, i.e., the dangling bond, therein and is oxidized. Thereby, the nano-tube becomes able to be easily severed at the non-bonded hand without deteriorating the nano-tube. As a result of this, the length of the nano-tube is shortened, and the mutual entangles between or among the nano-tubes are lessened. If using this nano-tube as the emitter, the surface of the emitter has an improved flatness.
A fabrication method of a nano-tube according to the second aspect of the invention is constructed in a form wherein, in the fabrication method of a nano-tube according to the first aspect of the invention, in the ion radiating step, after an element had been ionized, the resultant ions are accelerated by an electric field and thereby radiated onto the nano-tube.
A fabrication method of a nano-tube according to the third aspect of the invention is constructed in a form wherein, in the fabrication method of a nano-tube according to the first aspect of the invention, an element had been reduced into plasma condition and the ions that have been produced in the plasma condition creating process, are radiated onto the nano-tube.
A fabrication method of a nano-tube according to the fourth aspect of the invention comprises the step of heating the nano-tube at a temperature of from 300 to 800xc2x0 C., and radiating ions onto the nano-tube thus-heated.
A fabrication method of a nano-tube according to the fifth aspect of the invention comprises the step of heating the nano-tube at a temperature of from 300 to 800xc2x0 C., and radiating an atomic state of atoms and ions onto the nano-tube thus-heated, simultaneously.
A fabrication method of a nano-tube according to the sixth aspect of the invention comprises the step of heating the nano-tube at a temperature of from 300 to 800xc2x0 C., and radiating ions onto the nano-tube thus-heated, and oxidizing the nano-tube.
A fabrication method of a nano-tube according to the seventh aspect of the invention comprises the step of placing the nano-tube on a glass substrate, heating the nano-tube at a temperature of from 300xc2x0 C. to a temperature lower than a distortion point of the glass substrate, radiating ions onto the nano-tube thus-heated, and oxidizing the nano-tube.
A fabrication method of a nano-tube according to the eighth aspect of the invention comprises the step of heating the nano-tube at a temperature of from 300 to 800xc2x0 C., radiating ions and an atomic state of atoms onto the nano-tube thus-heated, simultaneously, and oxidizing the nano-tube.
A fabrication method of a nano-tube according to the ninth aspect of the invention comprises the step of placing the nano-tube on a glass substrate, heating the nano-tube at a temperature of from 300xc2x0 C. to a temperature lower than a distortion point of the glass substrate, radiating ions and an atomic state of hydrogen onto the nano-tube thus-heated simultaneously, and oxidizing the nano-tube.
A fabrication method of a nano-tube according to the tenth aspect of the invention comprises the step of radiating ions onto the nano-tube, heating the nano-tube at a temperature of from 300 to 800xc2x0 C., and radiating ions onto the nano-tube thus-heated.
A fabrication method of a nano-tube according to the eleventh aspect of the invention comprises the step of radiating ions onto the nano-tube, heating the nano-tube at a temperature of from 300 to 800xc2x0 C., and radiating ions and an atomic state of atoms onto the nano-tube thus-heated, simultaneously.
A fabrication method of a nano-tube according to the twelfth aspect of the invention is constructed in a form the nano-tube is a carbon nano-tube.
A manufacturing method of a field-emission type cold cathode, the manufacturing method comprising an emitter containing therein nano-tubes, an insulating layer and gate electrode provided so as to surround the emitter, and an anode electrode provided on the gate electrode to thereby cause an emission of electrons from the emitter by applying a voltage to the emitter, the method comprising the steps of, introducing a gas onto the emitter, applying a voltage to one of the gate electrode, the anode electrode, and a newly provided electrode to thereby cause an emission of the electrons, ionizing the gas, and radiating the ions onto the nano-tubes.
A manufacturing method of a field-emission type cold cathode, the manufacturing method comprising an emitter containing therein nano-tubes, an insulating layer and gate electrode provided so as to surround the emitter, and an anode electrode provided on the gate electrode to thereby cause an emission of electrons from the emitter by applying a voltage to the emitter, the method comprising the steps of, introducing a gas onto the emitter, applying a voltage to one of the gate electrode, the anode electrode, and a newly provided electrode to thereby cause an emission of the electrons, ionizing the gas, radiating the ions onto the nano-tubes, and oxidizing the nano-tubes.
In the method for producing the field-emission type cold cathode in the past, it is possible to form a flat emitter and, in addition, a great number of the severed portions are formed. Thereby, the portions from which electron are emitted is become large in number, and a high performance of the emission and an increase in number of the emission points within the emitter are realized. Resultantly, the uniformity is enhanced. Resultantly, it is possible to cause the generation of a uniform and stable high-emission current.
A manufacturing method of a display device, the display device being a flat-surface type, according to the fifteenth aspect of the invention, comprises the fabrication method of a nano-tube according to one of the first to twelfth aspects of the invention, and/or, the manufacturing method of a field-emission type cold cathode according to the thirteenth or fourteenth aspect of the invention.